The invention relates to an ultrasonic sensor for sensing a spatial area and/or for contact-free distance measuring with at least one ultrasonic transducer for sending ultrasonic impulses and/or receiving the echo of ultrasonic impulses and a device for concentrating the energy of the ultrasonic impulses onto the spatial area to be sensed, respectively, of the energy of the echo of the ultrasonic impulses onto the ultrasonic transducer or transducers.
An ultrasonic sensor comprises, for example, at least one ultrasonic transducer which transforms electrical energy into sound and, in reverse, sound into electrical energy, a housing enclosing the ultrasonic transducer or transducers, an electrical connection and, optionally, an electronic circuit for signal processing also enclosed in the housing.
In order to sense a spatial area, respectively, to measure the distance between two points, conventionally an ultrasonic sensor is positioned at a suitable point and is directed onto the corresponding spatial area which is to be sensed, respectively, in which a body to be detected is present the distance of which to a reference point is to be determined. The ultrasonic sensor comprises an ultrasonic transducer which emits ultrasonic impulses and, optionally, receives the echo of the ultrasonic impulses reflected at the body. In the case of receiving an echo, the distance between the ultrasonic sensor and the body positioned within the spatial area that has been detected is determined with a computing circuit (echo propagation time measurement). Instead of an ultrasonic transducer a plurality of such ultrasonic transducers can be used whereby the function of the respective ultrasonic transducer may be limited to emitting the ultrasonic impulses, respectively, to receiving the echo of the ultrasonic impulses.
An ultrasonic sensor is known from German Patent Application 42 18 041 A1. An ultrasonic sensor for distance measurement comprises at least one ultrasonic transducer for sending a working sound impulse and for receiving the echo. The ultrasonic transducer is surrounded by a sound deflecting surface onto which the ultrasonic impulses of the ultrasonic transducer are impinged. In the sound reflecting surface a further ultrasonic transducer is arranged. It, in connection with a computing unit arranged downstream, has the task to monitor the ultrasonic transducer with respect to its proper function. In the disclosed sound deflecting surface the sound field is substantially only deflected. However, the sound field is not shaped and oriented in a defined manner.
Conventional ultrasound sensors have for certain applications the disadvantage that their sound field is of radial symmetry. Such ultrasonic sensors are, for example, mounted in or at the rearward bumper of a passenger car in order to indicate to the driver, when backing up, possible obstacles behind the vehicle. For this purpose, the ultrasonic sensors are, in general, controlled by a central control device which controls the sensors and processes the echo signals. Depending on the measured distance, an optical and/or acoustic signal is delivered to the driver. The ultrasonic sensors are designed to sense gap-free the area behind the vehicle across the entire vehicle width up to a distance of, for example, 180 cm. Since however low curbs or rough street surfaces should not deliver a signal, a plurality of ultrasonic sensors are required due to the radial-symmetrical sound fields of conventional ultrasonic sensors.
In order to provide for the best possible ground clearance, it would be necessary to employ a plurality of ultrasonic sensors with sound cones as narrow as possible. However, this is disadvantageous because of the high cost for the ultrasonic sensors and detrimental to the visual impression of the vehicle. Today's solutions provide a comprise of gap-free sensing with sufficient ground clearance and number of ultrasonic sensors required therefore.
In order to define the requirements in regard to such a parking aid, also called maneuvering warning device, the German Institute of Standards e.V. DIN has produced a standard suggestion for use with payload vehicles. In the standard proposal DIN 75 031 of May 1993 especially the requirements for the spatial area to be monitored behind the vehicle were determined. To this date, no ultrasonic sensors are available on the market which fulfill the requirements disclosed therein.
It is an object of the invention to provide an ultrasonic sensor with defined asymmetric radiation characteristic and a device for monitoring the proper function of the ultrasonic sensors as well as to suggest suitable applications of the ultrasonic sensors.
It is desired that the sending and receiving characteristic have sharp contours. It is also desired that the emitted sound field of the ultrasonic sensors in the case of spatial monitoring at vehicles, especially for exterior space monitoring, be embodied such that the detection range at the side facing the ground surface is substantially parallel and allows enough ground clearance. At the same time, the ultrasonic transducer should be small in size in order to allow the mounting at different locations, without requiring retrofitting or considerable adaptations of the location to the ultrasonic sensor as has been conventionally necessary.